Cholecystokinin (CCK): Physiology and What Studies Report

What cholecystokinin is

Cholecystokinin (CCK) is a peptide hormone and neuropeptide first characterised by its ability to contract the gallbladder — the name literally refers to moving the bile sac. A biochemistry review described CCK as a hormone produced chiefly by enteroendocrine I-cells of the duodenum and jejunum, released in response to luminal fat and protein, and circulating in several molecular forms derived from a common precursor (PMID 30480943). The same review outlined its classical digestive actions, including stimulation of pancreatic enzyme secretion, gallbladder contraction, relaxation of the sphincter of Oddi, slowing of gastric emptying and contribution to meal-related satiety signalling (PMID 30480943).

CCK is also expressed in the central and enteric nervous systems, where the sulfated octapeptide fragment (CCK-8) is a common active form. This page is for educational purposes only and is not medical advice; consult a licensed physician about any medical question.

Two receptors: CCK1 (CCK-A) and CCK2 (CCK-B)

CCK acts through two class A G protein-coupled receptors. Researchers solved structures of the human cholecystokinin receptors bound to agonists and antagonists, and the study described how the two subtypes recognise peptide ligands and small molecules and how sulfation of the peptide influences binding, providing a structural basis for subtype selectivity (PMID 34556863). That structural work is frequently cited as a framework for understanding why some experimental ligands act preferentially at one receptor over the other.

Gallbladder physiology and biliary imaging

The best-established action of CCK is on the gallbladder. A 2024 review examined cholecystokinin and the CCK-A receptor in the context of biliary dyskinesia and discussed the receptor as a candidate target in disordered gallbladder motility (PMID 38314130). Because CCK reliably drives gallbladder contraction, a synthetic CCK analogue is used diagnostically during hepatobiliary scintigraphy to provoke emptying and measure the gallbladder ejection fraction.

One study analysed the kinetics of gallbladder emptying during CCK cholescintigraphy and framed the shape of the emptying curve as an indicator of in vivo hormonal sensitivity rather than a single end-point number (PMID 31604888). A separate report on optimal hepatobiliary scintigraphy for gallbladder dyskinesia examined how protocol choices affect interpretation of the test (PMID 33569543). Both papers illustrate a recurring theme: the measured response to CCK depends heavily on how the hormone is delivered and how the images are analysed, so results are not directly comparable across protocols.

CCK signalling outside the digestive tract

Cardiac pacemaker cells

Work published in Frontiers in Physiology reported that cholecystokinin-A signalling regulates the automaticity of pacemaker cardiomyocytes, linking CCK1 receptor activity to the rate at which these specialised cells fire (PMID 38179138). An earlier preprint of the same investigation described the same finding in cardiac pacemaker cell models (PMID 36747643). Separately, researchers examined cholecystokinin expression in the development of myocardial hypertrophy and reported changes in CCK expression associated with hypertrophic remodelling (PMID 34497680). These are laboratory findings about receptor biology, not clinical treatment data.

Airways and obesity

A 2023 Nature Communications study reported that antagonising the cholecystokinin A receptor in the lung attenuated obesity-induced airway hyperresponsiveness in an animal model, identifying pulmonary CCK1 receptor signalling as a contributor to excess airway constriction in that setting (PMID 36599824). The study illustrates that CCK receptor biology extends well beyond the gut and that, in some tissues, blocking the receptor rather than activating it was the manipulation researchers explored.

Pain pathways

A review in Neurobiology of Pain focused on CCK2 receptors in chronic pain and described CCK2 signalling as a modulator of nociceptive processing, including its discussed relationship with opioid analgesia and the persistence of pain states (PMID 35571964). This is the receptor subtype most associated with central nervous system effects of CCK.

Retinal cells

In a cell-based experiment, the cholecystokinin octapeptide was reported to antagonise apoptosis in human retinal pigment epithelial cells, which researchers interpreted as evidence of a cytoprotective action of CCK-8 in that model system (PMID 25221599/). Findings in cultured cells do not establish effects in intact organisms.

Dietary compounds and gut signalling

Related gastrointestinal signalling research has examined food-derived molecules: one study reported that gingerol activated the noxious cold ion channel TRPA1 in the gastrointestinal tract (PMID 27473961). It is cited here as context for how luminal chemical stimuli are sensed in the gut, the same environment in which CCK-releasing I-cells operate.

CCK in Research Settings: What Studies Report

The verified literature summarised on this page consists largely of mechanistic, structural, imaging and animal studies rather than safety trials, and none of the cited papers presented a systematic tabulation of adverse events. What the papers did report is that the measured biological response to CCK varies with delivery and context: the study of emptying kinetics during CCK cholescintigraphy emphasised that the rate and pattern of gallbladder contraction reflect in vivo hormonal sensitivity and can differ between individuals (PMID 31604888), and the scintigraphy protocol analysis reported that methodological choices influence whether a gallbladder is classified as dyskinetic (PMID 33569543).

Because CCK1 receptors are present in non-digestive tissues such as pacemaker cardiomyocytes (PMID 38179138) and airway tissue (PMID 36599824), researchers have noted that receptor-directed interventions would not be expected to act on a single organ in isolation. Questions about diagnostic or therapeutic use of any CCK-related agent belong with a licensed clinician.

How to read this evidence

• Different receptor, different story. Papers about CCK1 and CCK2 describe different biology; the structural study mapped both subtypes and their distinct ligand interactions (PMID 34556863).
• Model matters. Cultured retinal cells (PMID 25221599) and rodent airway models (PMID 36599824) generate hypotheses, not human outcomes.
• Agonism versus antagonism. Some findings involve stimulating the receptor and others involve blocking it, so direction of effect cannot be assumed from the hormone's name alone (PMID 38314130).

References

• Biochemistry, Cholecystokinin (StatPearls)
• Structures of the human cholecystokinin receptors bound to agonists and antagonists (Nature Chemical Biology, 2021)
• Cholecystokinin and cholecystokinin-A receptor: An attractive treatment strategy for biliary dyskinesia? (World Journal of Gastroenterology, 2024)
• Kinetics of Gallbladder Emptying During Cholecystokinin Cholescintigraphy as an Indicator of In Vivo Hormonal Sensitivity (Journal of Nuclear Medicine Technology, 2020)
• Optimal hepatobiliary scintigraphy for gallbladder dyskinesia (Surgery Open Science, 2021)
• Cholecystokinin-A signaling regulates automaticity of pacemaker cardiomyocytes (Frontiers in Physiology, 2023)
• Cholecystokinin-A Signaling Regulates Automaticity of Pacemaker Cardiomyocytes (bioRxiv, 2023)
• Antagonizing cholecystokinin A receptor in the lung attenuates obesity-induced airway hyperresponsiveness (Nature Communications, 2023)
• CCK2 receptors in chronic pain (Neurobiology of Pain, 2022)
• Cholecystokinin Expression in the Development of Myocardial Hypertrophy (Scanning, 2021)
• Cholecystokinin octapeptide antagonizes apoptosis in human retinal pigment epithelial cells (Neural Regeneration Research, 2014)
• Gingerol activates noxious cold ion channel TRPA1 in gastrointestinal tract (Chinese Journal of Natural Medicines, 2016)